A hollow-fiber membrane is a hollow capillary tube in which the wall functions as a permeable, non-permeable, or semipermeable membrane depending upon the application. In many cases, hollow fibers are used as cylindrical membranes that permit selective exchange of materials across the walls. They may also be used as containers to effect the controlled release of a specific material or as reactors to chemically modify a permeant as it diffuses through a chemically activated hollow-fiber wall. Hollow fiber technology has recently become useful for the production of permselective, biocompatible immunoisolatory vehicles. These hollow fiber vehicles may contain materials such as living cells, proteins, or medicaments. They are designed so that material within the hollow fibers can permeate through the walls of hollow fiber vehicle. In use, the hollow fiber vehicles are delivered to a site specific in the body in need of the particular material present in the core of the hollow fiber. Specific applications for which such hollow fibers may be useful include restoration of insulin production and the treatment of neurotransmitter-deficiency diseases such as Parkinson's disease by delivery of a particular neurotransmitter to a site specific in the body. See, for example, U.S. Pat. No. 4,892,538.
No matter what the particular application of the hollow fiber vehicles, the morphology and thickness of the fiber membrane must be controlled to obtain the desired mechanical and transport properties suitable for the particular application.
There are four conventional synthetic-fiber spinning methods that may be used to produce hollow-fiber membranes: (1) melt spinning; (2) dry spinning; (3) wet spinning; and (4) a combination of dry and wet spinning. In each of these meth- ods, a tubular cross-section of the hollow fiber is formed by delivering a spinning material such as a polymer, copolymer, cellulosic material, or the like, through a spinneret nozzle while simultaneously delivering a material to be housed in the core of the fiber. Spinneret nozzle assemblies exist in a variety designs such as those shown in U.S. Pat. Nos. 4,035,459; 4,127,625; 4,229,154; 4,322,381; 4,323,627; 4,342,711; 4,380,520; and 4,744,932.
Some of the problems associated with these prior art nozzle assemblies and hollow fiber forming techniques include an inability to form fibers from highly viscous thermoplastic polymers due to nozzle clogging, an inability to adjust the nozzle assembly to produce varying membrane thicknesses and morphologies, an inability to change nozzle types or nozzle caps in the assembly so as to allow for the production of different types and shapes of hollow fibers, and an inability to produce Z-fibers having trabeculae oriented substantially longitudinally within the fiber wall and substantially interconnected with one another within the fiber wall.
U.S. Pat. No. 3,871,950 discloses hollow fiber membranes having a gradient of pore sizes on the outer or on the outer and inner surfaces. There are no interconnections between the porous regions along the long axis of the fiber. As such, the fiber is a succession of closed voids oriented along the long axis of the fiber. The membranes of the present invention, however, have a different morphology in which trabeculae within the fiber wall are substantially interconnected with one another and some or all thereof are continuous with the outside of the fiber.
General background information in the field of this invention may be found in U.S. Pat. No. 4,385,017, EP,A 0 277 619, and JP,A 57 106 708. Accordingly, it is an object of the present invention to produce a nozzle assembly that can be used with various materials having different and widely varying viscosities.
It is another object of the present invention to provide a nozzle assembly of modular construction wherein parts of the assembly can be easily replaced and substituted for, so as to facilitate the production of hollow fibers of different sizes, shapes, membrane thicknesses, and surface morphologies.